Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data. In general, the wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmission power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc.
To overcome performance deterioration caused by channel fading of wireless communication, many researches have been conducted on spatial diversity and/or spatial multiplexing using a multiple input multiple output (MIMO) system. The MIMO system is implemented such that a transmitter and a receiver have two or more antennas, thereby providing advantages such as a high data rate, reliability improvement, channel capacity increase, etc.
In the wireless communication system, a user equipment (UE) performs cell search for initialization or handover. For example, after power is on, the UE performs initial cell search to select a cell for initially receiving a service. The cell search is a process for attaining downlink synchronization and for attaining a cell identifier (ID). A signal used in the cell search is called differently according to a system, such as a synchronization channel, a synchronization signal, a midamble, and a preamble.
A universal mobile telecommunications system (UMTs) of 3rd generation partnership project (3GPP) based on wideband code division multiple access (WCDMA) divides 512 long pseudo noise (PN) scrambling codes into 64 code groups to facilitate the cell search, and uses a primary synchronization channel and a secondary synchronization channel. The primary synchronization channel is used by the UE to attain slot synchronization. The secondary synchronization channel is used to attain frame synchronization and scrambling code groups.
Evolved-UMTS (E-UMTS) of 3GPP is called long term evolution (LTE), and a primary synchronization signal and a secondary synchronization signal are used in the cell search. The section 6.11 of 3GPP TS 36.211 V8.2.0 (2008-03) “Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)” may be incorporated herein by reference. The primary synchronization signal uses three synchronization sequences to indicate a cell group ID. The secondary synchronization signal indicates one of 168 cell IDs. Therefore, by using the primary synchronization signal and the secondary synchronization signal, one of 504 cell IDs in total can be identified.
Institute of electrical and electronics engineers (IEEE) 802.16e is also called WiMax, and uses a preamble that appears in the first position of each frame in the cell search. The preamble consists of a subcarrier set configured with a spacing of three subcarriers in a frequency domain, and has a characteristic in that the same waveform is repeated 3 times in a time domain. Further, neighboring cells use different subcarrier sets.
The use of multiple antennas is inevitable in a next generation wireless communication system to increase spectral efficiency. Since transmit power of each transmit antenna is allocated constantly in a MIMO system in general, it is preferable to utilize all of the multiple antennas to maximize output power in a transmitter. However, the multiple antennas are not considered in the aforementioned cell search process in the conventional wireless communication system.
Therefore, there is a need for a method capable of supporting multiple antennas in a cell search process.